Diagnosis And Testing - Electric Back Light (EBL) System

Operation of the EBL system can be confirmed by the following:

1. Use a scan tool and check for Diagnostic Trouble Codes (DTCs) monitored by the Heating Ventilation and Air Conditioning (HVAC) Module. If any DTCs are found, repair as required. Depending on the DTCs, the rear defog may not be allowed to activate.
2. Turn the ignition to RUN and press the rear window defogger switch to ON. Rear window defogger operation can be checked by feeling the surfaces of the rear window glass. A distinct difference in temperature between the grid lines and the adjacent clear glass should be detected within three to four minutes of operation.
3. If a temperature difference is not detected, use a 12 volt Direct Current (DC) voltmeter and contact the rear glass heating grid terminal with the negative lead, and connector terminal with the positive lead. The voltmeter should read battery voltage. If the voltmeter does not read battery voltage, check the following:
   • Confirm the ignition is in RUN.
   • Confirm the rear window defogger switch is being read by the BCM (there is no DTC to indicate a failed switch or open switch connection). Using the scan tool find the rear defog monitor in the HVAC module data. Press and release the rear defog switch while monitoring; if the HVAC input monitor does not toggle (ON/OFF) repair the open connection between the switch and HVAC or replace the failed switch.
   • Confirm the EBL feed wire is connected to the heating grid positive terminal and that there is continuity between the heating grid and the EBL relay in the Power Distribution Center (PDC).
   • Confirm the EBL ground wire is connected to the heating grid negative terminal and that there is continuity to ground.
   • Confirm the EBL relay in the PDC is operational. Refer to the Wiring Information.
4. If broken defogger grid lines or bus bars are suspected, use a 12 volt DC voltmeter and contact terminal A with the negative lead and each rear glass heating grid line at its mid-point C with the positive lead. The voltmeter should read approximately 6 volts at each grid line mid-point. If the voltmeter does not read approximately 6 volts, repair the open grid line(s) or bus bar(s).